- Bright or high color temperature outdoor night lighting threatens bird health and safety
- The AMA warns that outdoor night lighting with color temperature greater than 3000 K is a danger to people, too
- Street lights that are no brighter than necessary, and has color temperature less than 3000 K, is safest for birds and people
Streetlights and Wildlife
Tom Jervis, President, Sangre de Cristo Audubon Society
In the 21st century, we are accustomed to think of light as something that happens when you flip a switch. But as recently as 100 years ago, artificial light was something that limited and dim. It was not until after the Second World War that the technology to generate vast quantities of electrical energy and transform that into astonishing levels of illumination, among other social benefits, became widespread. With the recent advent of inexpensive and highly efficient light-emitting diode (LED) technology, our capability to bring very high illumination levels took a great leap forward.
Wildlife evolved to live with the natural day-night cycle and seasonal variation in that pattern. Most living things, including humans and many plants, are exquisitely tuned to these circadian rhythms by internal clocks that keep our body processes functioning properly.
Modern LED technology, particularly high color-temperature (blueish) lighting, has created a serious problem for wildlife beyond that already created by our sprawl into areas not previously affected buy our civilization. There are two issues with area lighting such as streetlights. The first is the intensity of illumination and how well it is directed to those places where it is wanted and needed. LED lighting is generally better directed than the commonly used light fixtures of the recent past and it is easier to control to prevent “trespass light” going where it is not needed. Because it is so efficient, however, it is too easy to create a glare problem both for humans and for wildlife if direct and reflected light are too intense. The second issue with LED lighting has to do with the color temperature of the light. LEDs come in color temperatures from about 1000 K to 10.000 K or more. The higher the temperature, the more blueish the light is; the lower the temperature the more yellow to red it is. Note that this is independent of the intensity—usually measured in lux (lumens per square foot)—of the illumination.
For wildlife, particularly birds and insects, the problem is compounded by the color temperature of the lighting. Birds and insects “see” in the ultraviolet (UV) and high-color temperature lights contain significant UV light. Lights of any kind disturb the day-night rhythm that animals expect, but the intense blueish light of high temperature LEDs amplifies the effects.
Research has shown that blueish light from high color temperature LEDs is particularly disturbing to birds, many of whom migrate at night, navigating by the stars and Moon. They are confused by overly-bright lights, disrupting their migration patterns and causing them to be “trapped’ by these lights until they collapse from exhaustion. Higher levels of light pollution were associated with more species during migration—evidence that light pollution attracts migratory birds to cities across the U.S. Research has also found that cities contained the greatest numbers of migratory bird species during spring and autumn migration. This is cause for concern, as it shows that the influence of light pollution on migratory behavior is strong[i].
Research in Germany on the Blue Tit, a chickadee-like bird, has demonstrated that artificial lighting results in the males starting to sing earlier in the morning, and that females start to build their nests earlier in the season. The researchers also documented disruption in the mating behavior of the birds, resulting in more “extra pair” matings[ii].
Insects are also attracted to light, more so by light with a high UV content. Research has shown that populations of insects living near to artificial lights include more predator and scavenger species than populations living in similar, but darker, conditions. This shift can affect the survival rates of different species and have effects on birds and mammals that feed on those species. Interestingly, the effects were seen during the day, as well as at night, so these population shifts are ongoing[iii]. Mammals, many of whom are nocturnal, so bright artificial lighting, particularly high color-temperature LED lighting, is bad for them as well, disrupting their circadian rhythms, their foraging and hunting behaviors, and their ability to avoid predators[iv].
Finally, the American Medical Association (AMA) issued a rare warning and guidelines on how communities can choose LED streetlights to “minimize potential harmful human health and environmental effects.”[v] The AMA’s statement recommends that outdoor lighting at night, particularly street lighting, should have a color temperature of no greater than 3000 Kelvin (K).
So high levels of lighting, particularly UV-rich LED lights, is bad for animals disrupting the behaviors which evolution has prepared them for life in the world. But at the same time, we need artificial lighting for the protection of public health, safety, and security. Fortunately, there are solutions. The same technology that produces UV-rich and overly bright lights also makes it possible to make lights at a lower color-temperature with more than adequate intensity for public purposes. In a review of artificial lighting for the National Park Service[vi], the authors concluded that for the particular case of roadway lighting, that “Where light is essential, fixtures should be full cutoff and shielded to minimize glare from any non- road site …. The best overall choice for spectrum is probably yellow (e.g., low-pressure sodium or yellow/amber LED).”
The choice is ours to make. We can have the social benefits of artificial lighting with minimal disruption of the natural world if we choose the right lighting source. Low color temperature LEDs provide public safety and security and are efficient and low-cost to operate. That is the path we should take.
 Cities can help migrating birds on their way by planting more trees and turning lights off at night, <https://theconversation.com/cities-can-help-migrating-birds-on-their-way-by-planting-more-trees-and-turning-lights-off-at-night-152573>.
 Artificial night lighting affects dawn song, extra-pair siring success and lay date in songbirds, Bart Kempenaers, Pernilla Borgström, Peter Loës, Emmi Schlicht and Mihai Valcu, Current Biology, 20 1735, 2010.
 Artificial Night Lighting and Protected Lands : Ecological Effects and Management Approaches, Travis Longcore and Catherine Rich, Natural Resource Report NPS/NRSS/NSNS/NRR—2017/1493, National Park Service, Fort Collins, Colorado.